what was the point?

Maybe the point was just that the Doctor does so much good and he is seldom noticed apart from wispers and rumours in legends.

A hook for a future story with a future doctor, or just a nod to the fact that he has offscreen adventures (e.g. all the ones he mentioned when he met the ood at the beginning of part 1)

Personally I think it would be hilarious if we had a Mediaeval story, maybe something with the Black Death and at the end the construction of the stained glass window...

Surely "the point" was to emphasise that The Doctor is a traveller in time.

Black Death already covered in Peter Davisons 'The Visitation'

Just simply a way for Clare Bloom's character to appear to Wilf... and hint at the Doctor's return.

Or as some said to reference he comes and goes and is mentioned in rumours and legends, also a nod to The Satan Pit.

I can't remember which one, but one of the Big Finish audios has the TARDIS ending up in a stained glass window as a result of the adventure the Doctor is on - not that I think it is related, it just reminded me of it.

The story was that the Doctor saved the convent from something or other and this new church was built on the old convent site. I wasn't paying much attention as it was really boring.

It was something along those lines.

I thought it was a nice enough scene to be honest, good introduction to Claire Bloom's character and a good scene for Wilf to get a big slap of focus onto the Doctor. As far as unseen endeavours being touched upon go, I think this one had a bit more weight and worked nicely.